In general, an air conditioning unit has doors for opening and closing openings, and such doors are operated through a linking device. For example, the linking device is constructed of resinous linking members, such as motor levers, an intermediate plate, rotation plates and a connecting plate (connecting member) that connects the rotation plates, so as to reduce weight and costs.
In a vehicle, the air conditioning unit is used in a condition in which ambient temperature widely changes from low temperature such as −30° C. to high temperature such as 80° C. The linking device needs to operate appropriately irrespective to the change of the ambient temperature. However, the resinous linking members are likely to thermally expand under high temperature.
FIG. 7A shows an example of a connecting plate 133, which is one of the linking members, under ordinary temperature. FIG. 7B shows the connecting plate 133 under high temperature. The connecting plate 133 is connected to the other linking members, such as the rotation plates, at connecting points 133c, 133d. When the connecting plate 133 is affected by heat, the length of the connecting plate 133 increases due to thermal expansion. That is, a distance D2 between the two connecting points 133c, 133d under the high temperature is greater than a distance D1 under the ordinary temperature.
The connecting plate 133 is generally relatively longer than the other linking members. Thus, the increase of the length of the connecting plate 133 due to thermal expansion is larger than those of the other linking members. If the door levers, which are connected to the doors, receive stress due to the thermal expansion of the connecting plate, the doors will be twisted. As a result, it will be difficult to sufficiently seal the openings by the doors.